Problem: Simplify the following expression: $n = \dfrac{1}{9p} - \dfrac{4}{9p}$
Explanation: Since the expressions have the same denominator we simply combine the numerators: $n = \dfrac{1 - (4)}{9p}$ Combine like terms: $n = \dfrac{-3}{9p}$ Simplify by dividing numerator and denominator by 3: $n = \dfrac{-1}{3p}$